Terahertz-range polar modes in domain-engineered BiFeO₃

The dielectric permittivity and properties of electrically active lattice resonances in nanotwinned BiFeO₃ crystals have been studied theoretically using an earlier established interatomic potential. The results suggest that an array of 71° domain walls with about 2–5 nm spacing enhances the static permittivity of BiFeO₃ by more than an order of magnitude. This enhancement is associated with an electrically active excitation, corresponding to a collective vibration of pinned domain walls at a remarkably high frequency of about 0.3 THz.

Description

Change of the (polar-active) phonon spectrum due to presence of dense domain-interface structure of BiFeO3 (right panel) in comparison with the single-domain case (left panel). Additional low-frequency Γ-point mode (labelled A) is responsible for 25x enhancement of permittivity in the domain engineered material.